The present invention relates to improved methods for preparation of N-(phosphonoacetyl)-L-aspartic acid, also known as PALA, in the form of the tetrasodium or disodium salt. More particularly, the present invention is concerned with a method for the large scale preparation of the tetrasodium salt and the disodium salt of N-(phosphonoacetyl)-L-aspartic acid.
The compound, N-(phosphonoacetyl)-L-aspartic acid (PALA), was first prepared as a rationally designed transition state analogue inhibitor of aspartate transcarbamylase, as described by Stark et al., J. Biol. Chem., 246, 6599 (1971). Subsequent publications have presented an improved synthetic scheme for gram amounts of PALA, and have demonstrated inhibition of pyrimidine nucleotide biosynthesis in vitro, as discussed by Stark et al., J. Biol. Chem., 249, 6945 (1974), as well as in vivo, as discussed by Yoshida et al., J. Biol. Chem., 249, 6951 (1974). PALA has been shown to be active against the B16, Lewis Lung, and P388 tumor systems, as indicated in the NCI screening program, Selected Agents List, Drug Evaluation Branch, DR and DP, Data through August 31, 1976, p. 143.
While the synthesis of PALA is straightforward, the preparation of the tetrasodium salt or the disodium salt in kilogram quantities has proven to be a major problem. The method of the present invention is particularly well suited for the production of such quantities. In copending U.S. Patent Application Ser. No. 851,382, filed Nov. 14, 1977, commonly assigned, there is described a method for the preparation of the tetrasodium and disodium salts of PALA, and this application is incorporated by reference herein.